Extremal graphs for the sum of the first two largest signless Laplacian eigenvalues

Zi-Ming Zhou, Zhi-Bin Du, Chang-Xiang He

For a graph $G$, let $S_2(G)$ be the sum of the first two largest signless Laplacian eigenvalues of $G$, and $f(G)=e(G)+3-S_2(G)$. Very recently, Zhou, He and Shan proved that $K^+…